Neural correlates of the emergence, stabilization and evaluation of conscious visual percepts

Awareness is one of the most intriguing functions of the human brain. Nevertheless, which neural mechanisms mediate it remains controversial. In the present fMRI experiment, we aimed to disentangle three models that predict that visual awareness arises from: 1) enhanced activity within the ventral stream (known to mediate object recognition); 2) information reaching the fronto-parietal network (known to mediate visuospatial processes and attention); or 3) the monitoring of one’s own attentional state, subserved by other brain areas, such as the superior temporal sulcus (STS) or temporo-parietal junction (TPJ). Visual awareness, defined as the subjective feeling of seeing, was evaluated with a gradual scale, from not seeing anything (rating 1), to seeing something that cannot be categorized (rating 2), to categorizing with low (rating 3) or high certainty (rating 4). Brain regions associated with awareness should display a gradual increase of activity as these ratings increase. Conversely, dichotomous activity (ratings 3&4 > 1&2) should reflect attentional mechanisms of percept stabilization. Finally, increased activity when one is certain (of seeing or not seeing) rather than uncertain (ratings 1&4 > 2&3) should be related to confidence. Gradual activity was found in a subset of fronto-parietal and higher-order visual areas, jointly contributing to the build-up of awareness. Dichotomous activity was found in fronto-parietal and early visual areas, confirming a stabilization mechanism, in which the attentional network modulates activity in early visual cortex. Finally, confidence-related activity was found in STS/TPJ. In conclusion, our study dissociates the closely related mechanisms of awareness, attention, and certainty.